1. Field of the Invention
The invention relates to a circular knitting machine particularly suited for the production of cut pile.
2. Description of the Prior Art
The integrated cutting of pile loops in the knitting machine is of particular commercial importance, as a subsequent cutting by a shearing process during finishing results in a high waste of pile material and requires additional finishing steps.
Known methods to solve this problem by severing pile loops in the knitting machine have fallen into four groups.
In the first group the pile loops are severed by being drawn over a sharp knife-like cutting edge which penetrates as a result of its extension into the pile loop and thus severs it. As for example is already known from U.S. Pat. No. 1,546,790, the cutting edge can be a an extension of the pile forming edge on a sinker which is positioned in a sinker ring. Similarly, the cutting edge can be provided at a pile element arranged in the cylinder in the manner described in West German Specification No. 2,917,378 or last German counterpart 138,227. The cutting edge is there inclined with respect to the direction in which the pile elements retract and is positioned so that the pile loop is drawn during the retraction of the pile element until it is severed on the cutting edge. Furthermore, such a cutting edge can be arranged on the shank of a hooked pile element underneath the hook, as is shown for example in West German Specification No. 2,704,295. The pile loop formed by the hook is pressed down by a holding down wheel while the pile element is raised to such an extent in which the cutting edge will tear the drawn loop while the needles remain in miss position. It is obvious that extending or stretching the pile loop to sever it raises to problems in a number of respects and as a result is relatively unreliable. Reliable severing can only be assured over long periods if pile material is used as fine as possible and having a low twist with a low tenacity and and also having a very limited elasticity, so that the pile loop is actually severed simply by drawing if over a cutting edge. Since the stretched pile loop slides over the cutting edge, the cutting edge is quickly worn, which results in broken pile elements and thus fabric faults, machine stoppage and high replacement costs for pile and/or cutting elements. These disadvantages can be avoided to a certain extent if an independently movable knife-like cutting member is arranged between adjacent pile elements or lamellae as taught in U.S. Pat. No. 4,026,126, which hold the pile thread extended for cutting by the moving cutting element. The movable cutting element is provided with an upper sloping cutting edge and is moved upwards between the pile elements (located in the cylinder) and between their hooks, in order to sever the pile loop increasing their extent. Although substantial wear might be expected, the above-mentioned disadvantages are substantially reduced in such a circular knitting machine, but other disadvantages result which will be further explained below.
In the second group of methods the pile loops are severed by being crushed by a crushing wheel. For example according to the teaching of U.S. Pat. No. 1,596,527, the pile loop is formed over a pile element located in the dial, the pile element is then supported from beneath and a crushing wheel is pressed on it from above, in order to crush the pile loop. In the example of U.S. Pat. No. 3,933,907 hooked pile elements located in the dial form the pile loop which is subsequently abraded by a crushing wheel. In British Pat. No. 891,937 the pile loop is formed over an arcuate sinker neb and slides rearwardly thereon by subsequent knitting operations, where it is engaged by a crushing wheel and abraded. Such crushing or abrading of pile loops can however only be satisfactorily accomplished if sufficient time is allowed for it. This is only possible with low speed machines. Special problems result when using high tenacity yarns.
In the third group of methods the pile loops are transferred to a separate cutting element where they are cut. One of the two portions of the pile loop is so offset with regard to the other--by a correspondingly formed dial according to British Pat. No. 813,357 or by a displacement wheel according to British Pat. No. 849,710--that a transfer element can be introduced into the pile loop, which serves as support during cutting. Such an insertion of cutting elements and supports into the pile loop is, however, only possible in coarse cut machines, as with finer cuts the two portions of the pile loop are too close to each other and cannot with the necessary degree of certainty be brought into such offset or staggered relationship.
In the fourth group of methods to sever pile loops, the severing is effected by two cutting edges movable relative to each other. In German Pat. No. 1,153,482, movable pile elements are arranged in the dial having upright projections on their outer ends with cutting edges on the dial side of the projections. In the same slots of the dial, side by side to the pile elements, fixed cutting elements are dispersed, projecting with their cutting edges on the outer ends of the dial. Pile loops are formed on the shanks of the pile elements adjacent the cutting edges and by retracting the pile elements and the loops, their cutting edge will contact the cutting edge of the cutting element and in cooperation they will cut the pile loops. In an improvement, known from West German Pat. No. 1,585,051, the cutting elements are slightly pre-bent, so that the cutting edges of the cutting elements are resiliently pressed against the cutting edges of the pile elements to avoid a deflection from the cooperating cutting edges under cutting conditions. It is also known from German Patent specification No. 2,423,700 to arrange a movable hooked pile element tightly in a U-shaped cutting element having cutting edges on both sides so as to cooperate with the cutting edge of the pile element which is a portion of the hook when the elements are moved relative each to each other subsequent to the knitting process.
As a result of the cooperation of two cutting edges when moving at least the pile elements unlike in the first group of methods with only one cutting edge, the serving is not realized by an increased extent of the pile loop, but rather by relative movement of the cutting edges without any substantial additional extending of the pile loop. Furthermore the pile loops do not need to run under tension over the cutting edges so that by virtue of a cutting concept with relatively movable cutting edges both the abrasion of the cutting edges by the rubbing effect of the pile loops is reduced and the abrading of the pile thread, completely or partly by drawing over the cutting edge is avoided when the pile loops are formed. However, one particular disadvantage of such an arrangement is that the pile elements and the cooperating cutting elements, which in the example of West German Patent specification No. 2,423,700 is moreover arranged on either side of the shank of the pile element, must be arranged in the same slot and be capable of relative movement therein. The relative movement of elements side by side presupposes that increased friction must not occur between the elements. The necessary tolerance for an easily relative movement is detrimental to the cutting process, since then the cutting edge and the cooperating cutting edge must either have a corresponding relative tolerance, as in the example of DE-OS No. 2,423,700, or they can be relatively easily flexed away from each other by the pile loop, as in the example of DE-PS No. 1,153,482. Even with elastic compression of the stationary cutting element towards the pile element as is provided in the example of DE-PS No. 1,585,051, such a gap cannot be avoided, as on account of the necessary relative movability only light elastic compression can be exerted, which then makes it possible to still deflect the cutting edge of the pile element from cooperating cutting edge. Thus as soon as the cutting edges exhibit first effects of wear and if additional interfering factors unavoidable in practice add their effects such as damage or even only contamination of the elements which are moved against one another such as by fibre dust or solidified lubricant, the pile loop is no longer cut, but merely jammed therebetween.
A still greater basic disadvantage of these methods of arranging at least two relatively movably side by side elements in the same slot that also is to be avoided in moving knife-like cutting element of U.S. Pat. No. 4,026,126 between adjacent pile elements lamellae directs in that it necessitates too coarse a cut of the machine. The overwelming majority of pile machines are built with 18 or 20 cut per inch (Imperial). Of the--at best--1.4 mm per needle available, 0.5 mm is already occupied by the cut itself. The pile elments must be extended between the needles, and an unavoidable predetermined space has to be left between the needles and the pile elements for looping the pile. On that account the pile element can only have a thickness of at most 0.5 mm. This results that in the examples of German Pat. Nos. 1,153,482 and 1,585,051 the pile elements and the cooperating cutting elements can only be at most about 0.25 mm thick. Because of this neither an adequate compression of the two cutting edges onto the other nor an adequate inflexibility of the cutting edges can be achieved, so that such small element thicknesses are not acceptable in practice. Thus a coarser cut of the knitting machine is required.
In all known possible methods of integrated severing of the pile loops into the knitting machine, there is the common problem produce a equal pile side and a uniform stitch structure, in which the base thread covers the pile thread on the stitch side by plating. When the needles are being extended, the stitches are enlarged by forcing the latch open and clearing the latch and also during retraction as the the needle hook is being pulled through. As the needle loops of the base fabric are connected wale-wise and course-wise, they afterwards re-assume their original form. If the pile loops, however, are severed subsequent to the knitting process, there is no longer any possibility of retraction of the enlarged stitch loops of the pile thread until a subsequent course is knit. When knitting, the pile threads into the needle stitches of the base fabric it is desired to produce a uniform pile and stitch structure which is effected when the pile loops are maintained at least partially until extended the stitches are cleared from the needles by the subsequent course, and therefor no further protruded needle loops of the pile-threads are avoided as a result of their frictional connection to the acting needles.
Several methods of preventing enlarged stitches are known. Some of them are disclosed in various embodiments of a known circular knitting machine according to West German Specification No. 2,918,203, in which the severing of the pile loops is also realized corresponding to the above-mentioned first group of known methods similar to the teachings of West German Specification No. 2,704,295, so the the pile elements, after clearing the stitches of the previously knitted course from the needles, the needles are moved and the pile loops are severed by a cutting edge disposed opposite the hook opening and cooperating with a blade, pressing the pile loops against the dial. The elements are therefore arranged in the dial. According to the embodiment of FIGS. 2 to 9 of West German Specification No. 2,918,908 and also according to the teaching of East German Specification No. 136,227 or U.S. Pat. No. 1,596,527, subsequent to each pile course, a single threaded course is knit to clear the pile threads from the needles. Because of this, the pile is naturally less dense while the number of pile loops projecting from the base fabric is halved. According to the embodiment of FIGS. 10 to 19 of West German Specification No. 2,918,903 two pile hooks are arranged in each slot of the dial which alternately form and sever the pile loops; this results as explained above in detail with a coarse cut of the machine according to the required measurement of the pile elements, and moreover mutual interference between the pile elements and jamming of the pile loops may occur instead of its being severed. According to the embodiment of FIGS. 20 to 25 of West German Specification No. 2,918,903 and to the teaching of West German Specification No. 1,153,482 each course is knit only have a portion of the needles and pile elements; because of this, however, only a portion of a course is knit which is completed by the subsequent feeder and the productivity of the knitting machine is halved.
A fundamentally different possibility for a reprotruding the stitches of the pile thread by extending the pile loops is known from British Pat. No. 891,973 which belongs to the above described second group of methods and in which the pile loops are formed over curved sinker nebs in the dial, but are not severed immediately after their formation. Rather the pile loops slide rearwardly on the curved sinker neb while subsequent pile loops are knitted. Each pile loop is severed by means of an abrading wheel when the subsequent stitch of the pile thread has been completely knocked over, so that the severed pile loop then clears the sinker neb and can be pulled off by the fabric take-down. The curvature of the sinker neb is chosen so that the take-down friction causes the knitted pile loops to slide into the area of the abrading wheel. This requires the actual pile forming edge of the curved sinker neb be substantially horizontal or only slightly inclined to prevent the pile loops from sliding away undefined when they are formed by the cylinder needles. At the same time, the fabric take-down friction, acting in the same direction, must also effect a sliding movement of the pile loops along the curved sinker neb, even through the take-down strength acts substantially normally to the pile forming edge where the pile loop is formed on the sinker neb. In this manner the pile loops on the sinker nebs substantially hinder take-down and require high take down strength without precluding disturbances if e.g., different yarns with different friction on the sinker nebs are to be used. The high strength acting on the sinker nebs, to which must yet be added the pressure of the crushing wheel, necessitated a rugged construction for the sinker nebs which again results in the need to have a correspondingly coarse cut of the machine.
Naturally, the knitting latch needles have no effect on the pile threads if these are knitted into the base fabric by tuck stitches, described in the example of U.S. Pat. No. 2,933,907, West German Specification No. 2,704,295, West German Specification No. 2,423,700 and U.S. Pat. No. 4,026,126. By virtue of substantially extending free cutting of the pile loops according to the present invention, protruding pile loops are prevented so the pile thread is knitted to tuck stitches.